Electrical installations frequently provide electrical apparatuses requiring a three-phase electrical supply. For example, many electrical motors are supplied electrically by such three-phase voltages which generate three-phase load current. The frequency and the amplitude of the three-phase current is therefore regulated by the electrical installation as a means of commanding the operation of the electrical apparatus. The frequency and the amplitude of the three-phase current influence directly the operation of the electrical apparatus: for example, in the case of permanent-magnet synchronous motors, the rotation frequency of the motor is equal to the current frequency divided by the number of pairs of poles in the motor.
As a consequence, such electrical installations usually provide a three-phase electric inverter generating the three-phase current, and the inverter is controlled by a control device driving the amplitude of the three-phase current.
However, the electrical apparatuses known in the state of the art are not reliable. Indeed, the three-phase current generated by the inverter is not very well controlled. More precisely, the control devices currently used cannot regulate perfectly all frequency ranges. Consequently, the three-phase current often contains undesired harmonics, having frequencies out of the control device's frequency range. These harmonics may be caused, for example, by “DC bus voltage ripple”, in which a DC current supplied to the inverter has a small residual temporal variation, or during the operation of the inverter.
Such undesired harmonics may lead to undesired heating of the electrical apparatus, sometimes damaging or even destroying the apparatus. In order to avoid such damage, electrical apparatuses, and especially motors, are designed according to demanding guidelines to provide for high redundancy and important security margins. Their manufacture is consequently complicated, and their price increased.